1. Field of the Invention
The invention relates to a wheel centering device and more particularly to such a device in a motor vehicle test system.
2. Prior Art
Motor vehicle test systems have long been used to test performance of various vehicle subsystems in a controlled environment simulating actual road conditions. One known motor vehicle test system comprises a test platform for supporting the drive wheels of a vehicle under test in contact with what is known as a dynamometer roll. The dynamometer roll may be used to sense the power output of the drive wheels or to apply a variable load condition to the wheels to simulate a variety of driving conditions. Engine emission testing is commonly performed on such a test platform. The tests are made under a number of different conditions, such as cold engine, hot engine, light load, heavy load, etc. In order to obtain accurate measurements in the same tests performed on a number of different vehicles or on the same vehicle under different operating conditions, it is essential that the test platform conditions do not change from test to test. It has been found, for example, that test results are influenced by a change in the position of the wheels of the vehicle relative to the dynamometer roll.
A number of different arrangements for positioning the wheel of the vehicle on a dynamometer roll are known from the prior art. Some prior art systems employ a dynamometer roll and an idler roll spaced apart from the dynamometer roll, with the wheel of the vehicle supported on both rolls. In another arrangement, a pair of idler rollers are used, in front and behind the wheel, to position the wheel such that a top portion of the dynamometer roll makes contact with a bottom portion of the wheel. A problem of these and other prior art arrangements is a lack of control over the precise positioning of the vehicle wheel with respect to the dynamometer roll. Since even a slight variation in the relative position of the dynamometer roll and the wheel can significantly affect test results, a device for accurately controlling the positioning of the wheel is needed.